English is not my primary language,so that might be the issue,anyway,here it is:

Create a class X and declare(don't define) a private copy-constructor.Make a public clone() function as a const member function that returns a copy of the object that is created using new.Now write a function that takes as an argument a const X& and clones a local copy that can be modified.

damn,can't believe i didn't remember that "this" is a pointer.So,using a dereferenced this solves the thing.Thanks

Wait a minute. Do you actually copy the content of your X in your clone() method, without sharing the data in the original X instance? Write the necessary parts of class X (some data to modify, the definition of the copy constructor) and tests to prove how your exercise behaves.